Investigation of Substrate Swell-Induced Defect Formation in Suspended Graphene upon Helium Ion Implantation

Graphene membranes with distributed defects have attracted widespread attention in ionic/molecular selective transport applications, but the controllable defect formation requires a comprehensive microscopic understanding of the energetic-ion–graphene interaction mechanism including graphene amorphization upon ion irradiation and its substrate influence. In this work, we experimentally investigate the effect of a substrate swell originating from gallium focus ion beam fabrication on defect formation in suspended graphene with bilayer domains upon helium ion bombardment. Raman spectroscopy is used to correlate graphene defects with the red shifts and peak splitting phenomenon in the suspended graphene membrane. The correlations between Raman shifts at G and 2D peaks show that graphene strain played a dominant role in the interaction between helium ions and suspended graphene membrane. The formation of graphene defects upon helium ion implantation was related to the edge topography and sizes of the triangular hole structures. These provide insights into the influence of size-dependent substrate swells on defect formation in the suspended graphene membrane upon helium ion implantation. Our results can be used to analyze energetic-ion–membrane interactions in other suspended two-dimensional materials to enable controllable nanofabrication for ionic/molecular selective transport applications.